How does Ubers rating System algorithm work?
I highly recommend that you start reading on the Netflix challenge. It has tonnes of useful and interesting examples dealing with this sort of thing.
You will need an Algorithm that builds a score on both 'quality' and 'quantity'. That is, it needs to add a 'weight' to the final rating based on the number of reviews that an individual has. This is so that, for example, an individual with 50 8 score reviews would be rated higher than an individual with only one 9 score review.
I recommend that you implement Bayesian estimates to calculate weighted voting.
IMDb (Internet Movie Database) utilizes this algorithmn to determine its IMDB top 250 movies. (Robert C 2010)

The formula for calculating the Top Rated 250 Titles gives a true Bayesian estimate:
weighted rating (WR) = (v ÷ (v+m)) × R + (m ÷ (v+m)) × C
where:
R = average for the movie (mean) = (Rating)
v = number of votes for the movie = (votes)
m = minimum votes required to be listed in the Top 250 (currently 3000)
C = the mean vote across the whole report (currently 6.9)

Please note that in addition to the rating Algorithm, Uber has a dispatch algorithm which takes into consideration factors i.e. Drivers who are online and drivers who are nearest to the passenger.